> For the complete documentation index, see [llms.txt](https://v2.dataos.info/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://v2.dataos.info/consume/activate/apis/overview.md).

# Data application

A data application is an application built on top of a Data Product. It calls the Data Product's APIs and exposes the results to consumers: a KPI dashboard, an operational view, or any other application that makes the Data Product's outputs usable for a specific team or use case.

This section covers how to register and run that application in DataOS. The application can be built with any language or framework. You provide either a container image or an external URL. The steps are the same regardless of how the application is built.

## Two ways to surface a Data Product through an application

<table><thead><tr><th width="229.85894775390625">Pattern</th><th>Use when</th></tr></thead><tbody><tr><td><a href="/pages/tdJ0uwY3jeyyL3jD7EoO">Deploy a data application</a></td><td>DataOS runs the application from a container image.</td></tr><tr><td><a href="/pages/Gocd911eFoGEI9ofUdCy">Link an external application</a></td><td>The application is already hosted and running externally.</td></tr></tbody></table>

Both patterns create a catalog entry that links the application to its source Data Product. Consumers discover and open it from DataOS regardless of where it is hosted.

## How the Data Product connection works

The application connects to the Data Product through its API (for example, the Vulcan API). The API base URL and an auth token are passed to the application as environment variables. The manifest's `products` field links the application to the Data Product in the catalog.

<table><thead><tr><th width="239.16180419921875">What</th><th>How</th></tr></thead><tbody><tr><td>API connection at runtime</td><td>Environment variables in the manifest (<code>VULCAN_BASE_URL</code>, auth token)</td></tr><tr><td>Catalog relationship</td><td><code>spec.app.products</code> or <code>spec.link.products</code> in the manifest</td></tr></tbody></table>

## Resource types

<table><thead><tr><th width="249.5838623046875">Pattern</th><th width="117.29150390625">Resource type</th><th>What you provide</th></tr></thead><tbody><tr><td>Deploy a data application</td><td><code>app</code></td><td>A container image plus the command, port, and runtime configuration.</td></tr><tr><td>Link an external application</td><td><code>link</code></td><td>The hosted application URL.</td></tr></tbody></table>

## Next step

* To run your application on DataOS, follow [Deploy a data application](/consume/activate/apis/overview/deploy-a-data-application.md).
* To register an already-hosted application, follow [Link an external application](/consume/activate/apis/overview/link-an-external-application.md).


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